Imaging features of otosclerosis on photon counting detector CT: a retrospective case series and literature review.

BACKGROUND AND PURPOSE

Imaging findings of otosclerosis have been previously described using traditional energy integrated detector CT scanners. Recent developments in photon counting detector CT allow improved spatial and contrast resolution over previous technology.

METHODS

A retrospective observational case series review was carried out in 53 patients (106 temporal bones) who had imaging findings of otosclerosis. Imaging findings of otosclerosis were documented, including specific plaque location, the presence of otic capsule expansion, and IAC diverticula. The Symons and Fanning classification was used to categorize findings. The presence of the cochlear cleft was documented. 50 asymptomatic patients were reviewed to determine the presence of features that could be confounded for otosclerosis.

RESULTS

Per the Symons and Fanning classification, the following types were found in individual temporal bones: type 0-13, type 1-48, type 2a - 12, type 2b - 6, type 2c - 16, type 3-4. Seven patients had imaging findings that did not fit the classification criteria, primarily isolated otospongiotic plaques in other parts of the otic capsule. The fissula ante fenestram was involved in 91 otosclerosis and 4 temporal bones in asymptomatic patients. The cochlear cleft was visible in 3 otosclerotic and 10 normal temporal bones. Otic capsule thickness in symptomatic patients: concave - 52, flat - 27, convex - 24. In asymptomatic patients: concave - 98, flat - 2, convex - 0. IAC diverticula: present in 36% of otosclerosis and 2% of normal. Isolated foci of otospongiosis were identified in several patients without classic fenestral or retrofenestral disease.

CONCLUSIONS

Photon counting CT allows excellent visualization of otospongiotic plaques. Due to the high resolution, subclinical findings can be overlooked in asymptomatic patients and plaque may be visualized in the otic capsule that are not part of existing classification systems. The current study coincides with previous studies which demonstrate that otosclerosis may occur in any part of the otic capsule.